1. Field of the Invention
The present invention relates to a color toner for electrophotography, which is preferable as a toner for flash fixing and is able to form multi-color images, a combined set of color toners for electrophotography for forming multi-color images, in which several types of the corresponding color toner for electrophotography are combined, a color developing agent capable of forming multi-color images, which includes the corresponding color toner for electrophotography, a method and an apparatus for forming multi-color images, which use the corresponding color toner for electrophotography and are easily capable of forming multi-color images.
2. Description of the Related Art
In forming an image by electrophotography, generally, an electrostatic latent image carrier (which may be called a xe2x80x9cphoto conductorxe2x80x9d) is electrically charged to expose the corresponding electrostatic latent image carrier, thereby forming an electrostatic latent image. And, toner is adhered to the corresponding electrostatic latent image and is developed, thereby forming a visible image by a toner image. After the visible image brought about by the toner image is transferred onto a recording medium, it is fixed to form a fixed image on the recording medium
There are some fixing methods with respect to the fixing, one of which is a fusion fixing method by which toner for forming the visible image is solidified and fixed after the same is melted by compression and/or heating, and another of which is a flash fixing method by which toner for forming the visible image is solidified and fixed after the same is melted by irradiating light energy, etc.
Of these, the flash fixing method has been recently focused since the method has advantages in comparison with the fusion fixing method. That is, since the flash fixing method does not need any compression of the toner by bringing the toner in contact with a fixing roller, the image resolution (image reproducibility) is not deteriorated in fixing. Further, it is not necessary that the toner is heated and melted by a high temperature heating source, or the like since no high temperature heating source is required, it is possible to adequately prevent the inside temperature of an image forming apparatus from being increased, and even if recording paper is clogged in a fixing unit due to a cause of system failure, no concern is necessary for the recording paper to be ignited by the heat from the high temperature heating source. In addition, such a problem as fixing is not performed until a fixing roller reaches to a prescribed temperature does not exist, and thereby high-speed fixing is possible. Hence, various advantages may be earned.
However, in the case of the flash fixing method, although black toner having a high photoadsorption ratio has a satisfying fixing property, there is another problem in that the fixing property of color toner having a lower photoadsorption ratio is not necessarily sufficient.
Therefore, proposals for improving the fixing property by the flash fixing method in the corresponding color toner by doping an infrared ray absorbing agent to the color toner have been provided in patent publications for example in Japanese Patent Application Laid-Open Nos. 1985-63545, 1985-63546, 1985-57858, 1985-057857, 1983-102248, 1983-102247, 1985-131544, 1985-133460, 1986-132959, WO99/13382, 2000-147824, 1995-191492, 2000-155439, 1999-38666, 1999-125930, 1999-125928, 1999-125929, and 1999-65167, etc.,
However, as infrared ray absorbents that are doped to the color toner, for example, aminium-based, diimonium-based, and cyanine-based infrared ray absorbents (presenting light green color), polymetin-based, nickel complex-based infrared ray absorbents (presenting light brown color), a part of a cyanine-based infrared ray absorbent (presenting gray color), and lanthanoid-based infrared ray absorbent represented by tin oxide, ytterbium oxide, etc., (presenting white color), etc., have been publicly known. Of these, since a lanthanoid-based infrared ray absorbent displaying white has low infrared ray absorption power, the same absorbent cannot be used independently, for such reason, it is necessary that a colored infrared ray absorbent may be used along with the same lanthanoid-based infrared ray absorbent or the colored infrared ray absorbent may be used independently.
However, in a case in which a colored infrared ray absorbent is doped to the corresponding color toner that is used to form a color image expressing an optical color by laminating three types of color toner consisting of three prime colors, which are yellow toner, magenta toner and cyan toner, there is a serious problem in that the expression area of the color of the corresponding color toner is remarkably narrowed. That is, as shown in FIG. 11 and FIG. 12, (also, in these drawings, an xe2x80x9cINFRAREDxe2x80x9d means an infrared ray absorbent), where [L*], [a*], and [b*] (these indicate measurement values in compliance with the method for indicating object colors, which are regulated in Japanese Industrial Standards No. JIS Z 8729) in the publicly known three prime color toners, that is, yellow toner, magenta toner and cyan toner (each of which does not include any infrared ray absorbent) are compared with [L*], [a*], and [b*] in infrared ray absorbent-contained color toner, in which a colored infrared ray absorbent (Naphthalocyanine compound) is doped to each of the corresponding three prime color toners, the [L*i], [a*], and [b*] values of the corresponding infrared ray absorbent-contained color toner are narrowed due to influences of the infrared ray absorbent, wherein the brightness and chroma, etc., are narrowed, and the light transmission property is lowered. In this case, another problem arises in that the color becomes muddy.
Therefore, high performance color toners for electrophotography, which utilize the advantages in color toners and can solve the other problems, have not been developed until the present. There is a strong expectation for the production of such color toners for electrophotography
The present invention is to overcome the problems of the conventional arts and to meet requirements mentioned above. It is therefore an object of the present invention to provide a color toner for electrophotography, with which multi-color images can be formed, preferable as a flash fixing toner having an excellent fixing property, an excellent image resolution (image reproducibility) when fixed, an excellent color reproducibility in color overlapping, and exhibits excellent color tone, and meets high speed processing requirement; a combined set of color toners for electrophotography for forming multi-color images, in which a combination of the color toners for electrophotography is employed; a color developing agent containing the color toners for electrophotography, which is able to easily form high-quality multi-color images; and a method and an apparatus for forming color images, which are able to easily form high-quality multi-color images, using the color toner.
A color toner for electrophotography according to the present invention is used on the extreme bottom layer of a multi-color image which is comprised of laminating at least two types of toner selected from black toner, magenta toner, yellow toner, and cyan toner, and contains a coloring agent and an infrared ray absorbent, and whose contrast ratio is in the range of 35% to 95%. If the color toner for electrophotography is used for an fixing process utilizing light, high speed processing is enabled, and if the same is used on the extreme bottom layer in a multi-color image comprised by laminating color toners, do not affect color toners that are used on layers other than the extreme bottom layer. Further, the fixing property, image resolution (image reproducibility) at the time of fixing, and color reproducibility in color overlapping are excellent, and exhibit satisfying color tone.
A combined set of color toners for electrophotography according to the present invention is used to form a multi-color image comprised by laminating toners comprised of at least two types of color toners selected from black toner, magenta toner, yellow toner, and cyan toner, wherein at least one of the two types of toners which may be defined as toner A is used on the extreme bottom of the multi-color image and is selected from the magenta toner, yellow toner and cyan toner, and further contains a coloring agent and an infrared ray absorbent, and the contrast ratio thereof is 35% to 95%. In addition, the other toners used on layers other than the extreme bottom layer of the multi-color image which may be defined as toner B, are comprised of coloring agent and an infrared ray absorbent, and the contrast ratios thereof are 20% to 50%. If the combined set of color toners for electrophotography is used for a flash fixing process, high-speed processing is possible, and if one of the toners is used on the extreme bottom layer in a multi-color image and the other toners are used on layers excluding the extreme bottom layer, since the toners do not adversely affect each other, a high-quality image could be obtained in which the fixing property, image resolution (image reproducibility) in fixing, and color reproducibility in color overlapping are excellent, and exhibits satisfying color tone.
A color developing agent for electrophotography according to the present invention contains at least a color toner for electrophotography according to the present invention. If the color developing agent for electrophotography is used, the fixing property, image resolution (image reproducibility) in fixing, and color reproducibility in color overlapping are excellent, and satisfying color tone. Also, if the color developing agent for electrophotography is used for a flash fixing process, high-speed processing is possible.
A method for forming color images according to the present invention uses a color toner for electrophotography comprised of at least two types of color toners, which are selected from black toner, magenta toner, yellow toner and cyan toner, and at least one of these contains an infrared ray absorbent, in which one type selected from the magenta toner, yellow toner and cyan color is a color toner for the extreme bottom layer, having a contrast ratio in the range of 35% to 95%, and the method further comprises the steps of:
forming an electrostatic latent image on an electrostatic latent image carrier;
developing the above electrostatic latent image by using the color toner for the extreme bottom layer, forming a visible image on the extreme bottom layer by the color toner for the extreme bottom layer, further developing the electrostatic latent image by using a color toner for an upper layer other than the color toner for the extreme bottom layer in the color toners for electrophotography, and forming a visible image on the upper layer by the color toner for the upper layer;
transferring the visible image on the extreme bottom layer and the visible image on the upper layer onto a recording medium with the visible image on the extreme bottom layer placed on the extreme bottom layer, and forming a combined transferred image; and
transferring the combined transferred image onto the recording medium and flash fixing the transferred image.
In the image forming method, an electrostatic latent image is formed on an electrostatic latent image carrier in the step for forming an electrostatic latent image. In the developing step, the electrostatic latent image is developed by the color toner for the extreme bottom layer, and an visible image on the extreme bottom layer is formed by the corresponding color toner for extreme bottom layer. The electrostatic latent image is developed by using an toner for upper layer other than the color toner for extreme bottom layer in the color toners for electrophotography, and an visible image on the upper layer is formed by the corresponding toner for upper layer. In the transferring step, the visible image on the extreme bottom layer and the visible image on the upper layer are transferred onto a recording medium with the visible image on the extreme bottom layer placed on the extreme bottom, and a combined transferred image is formed. In the flash fixing step, the combined transferred image is transferred onto the recording medium, wherein the transferred image is optically fixed. As a result, a high-quality image having excellent image resolution (image reproducibility) and excellent color reproduction by color overlapping, a satisfying color tone may be efficiently formed.
A color image forming apparatus according to the present invention comprises: an electrostatic latent image carrier;
means for forming an electrostatic latent image on the corresponding electrostatic latent image carrier;
means for forming a visible image on the extreme bottom layer by developing the electrostatic latent image using a color toner for extreme bottom layer which is a color toner for electrophotography, comprised of at least two types selected from black toner, magenta toner, yellow toner, and cyan toner, in which one of the two color toners contains an infrared ray absorbent, and another one is selected from the magenta toner, yellow toner and cyan toner, and the contrast ratio thereof is 35% to 95%, and means for forming a visible image on the upper layer by developing the electrostatic latent image using an toner for upper layer other than the color toner for extreme bottom layer in the color toners for electrophotography;
means for transferring the visible image on the extreme bottom layer and the visible image on the upper layer onto a recording medium with the corresponding visible image on the extreme bottom layer placed on the extreme bottom layer, and for forming a combined transferred image; and
means for flash fixing the combined transferred image transferred on the recording medium.
In the apparatus for forming color images, the means for forming an electrostatic latent image forms an electrostatic latent image on an electrostatic latent image carrier. The means for developing the extreme bottom layer in the developing means develops the electrostatic latent image by using the color toner for extreme bottom layer and forms a visible image on the extreme bottom layer. The means for developing an upper layer develops the latent image by using an toner for upper layer and forms the visible image on the upper layer. The transferring means transfers the visible image on the extreme bottom layer and visible image on the upper layer onto a recording medium with the corresponding visible image on the extreme bottom layer placed on the extreme bottom layer and forms a combined transferred image. The flash fixing means flash fixes the combined image transferred on the recording medium. Consequently, a high-quality image that has excellent image resolution (image reproducibility) and color reproducibility in color overlapping and satisfying color tone can be efficiently formed on the corresponding recording medium.